Spreadsheets are great for creating secret codes and for breaking them. During World War II the German military used a machine they called Enigma to send coded messages. In a box about the size of a typewriter, wheels with letters on them were spun around to encode or to decode a message. The story of the breaking of that code by Alan Turing and the British code breakers was made into the movie The Imitation Game. We have used spreadsheets with some of their built-in rules to let you set up your own enigma machine. There are many ways you can use a spreadsheet to generate or to crack codes. It is fun to see if you can make a code your friends can’t break.